Formation of the Pagasa Wedge from 3-D Seismics, Southwest Palawan: 
Indications of a Major Mid-NeogeneTectonic Event

Aurelio, M.A.1, Forbes, M.T.2, Taguibao, K.J.L.1, Bacud, J.A.2, Savella, R.B.2

1National Institute of Geological Sciences, University of the Philippines
2 Philippine National Oil Company – Exploration Corporation

Abstract

3-D seismic profiles are used to characterize a tectonic wedge in offshore southwest Palawan. The relationship of the wedge with the underlying and overlying seismic units is studied to understand the implications of its formation in the regional tectonic evolution of the south Palawan – north Borneo area. This tectonic wedge, here named Pagasa Wedge, formed sometime in the Middle Miocene, following the underthrusting of the Nido Limestone below south Palawan. The initial stage of wedge formation involved ramping of the Early Miocene member of the Pagasa Formation over the Late Oligocene Nido Limestone along a detachment fault. This was followed by a thrust-fold event mainly affecting the Middle Miocene member of Pagasa. The uppermost sections of the wedge are filled with syn-thrust deposits. The top of the wedge is truncated by a major discontinuity that corresponds to the Middle Miocene Unconformity (MMU) observed to be widespread in the region. The thrust-fold structures that resulted from the formation of the wedge show favorable features of structural traps for petroleum accumulation.